The invention relates to an attachment for the paint cup of a well-known type of spray painting apparatus. The paint cup is secured to a spray gun and flow of pressurized air through or about the gun nozzle creates a partial vacuum at the fluid discharge orifice of the spray gun. Atmospheric pressure entering a vent opening in the lid of the paint cup acting upon the contents of the paint cup causes the paint to flow through a delivery tube to the fluid discharge orifice of the spray gun nozzle. The delivery tube is mounted on the lid or cover for the cup and is removable therewith, and the inner end of the delivery conduit extends to the bottom of the cup, usually adjacent the front wall thereof. The vent opening is normally formed in the lid or cover near an edge thereof as, for example, at the side.
The existence of the vent opening has in the past given rise to the danger of leakage through the opening onto the lid or cap, which in turn often dripped on the operator or the target, creating an undesirable condition which requires constant attention on the part of the operator. As the level of liquid in the paint cup is reduced the tendency to leak is, of course, also reduced so that many operators will only partially fill the cup thus effectively reducing the capacity of the system and requiring more frequent filling than usual.
It has been proposed to overcome the above disadvantages and to provide a system wherein leakage through the vent opening does not occur. This has been achieved by using a conduit or pipe threaded into the lid and effectively extending the vent opening so that the outer end of the vent opening is accessible to the interior of the paint cup through a trapped column of air even if the inner end of the conduit is below the liquid level. If the inner end of the conduit is above the liquid level, there will of course be no leakage. The pipe or conduit is arranged so that a column of air must be trapped before liquid can flow through the outer end of the vent opening. In use, the operator must return the cup to its upright position so that the conduit is above the liquid level. The foregoing is shown and described in the patent to Dalton Jr. U.S. Pat. No. 3,240,398.